Title Molecular surveys in 2-3 ``small'' samples from 0.5 to 3 msun
Pi A. Dutrey
Time 229 hrs
Molecular surveys in 2-3 ``small'' samples from 0.5 to 3 msun
Authors: A.Dutrey, M.Momose, S.Guilloteau, E. van Dishoeck
2. Science goal:
Study observable chemistry as complete as possible in a few
protoplanetary disks
orbiting stars from 0.5 to 3 msun. The goal is to estimate abundance
gradients, within
the disk and from object to object. It is required to disentangle
between excitation
conditions and abundance gradients by observing several transitions of
the same molecule.
A frequency survey AS COMPLETE AS possible - using all the
flexibility of
the correlator - is required.
The sensitivity required to complete such a survey is not easy to
derive. As a first
order, one can note that lines detected so far become optically
thick inside a radius
R1 ranging from 50 to 300 AU. With a power law of the surface
density, a line with
Tau=1 at 50 AU has Tau=0.07 at 300 AU. We thus select to work at
an opacity limit of
0.05 (1 sigma per channel). Moreover, we include a few much deeper
integrations in Band 6 to reach tau=0.02 and search for more complex molecules.
We select an angular resolution of
0.4", allowing to
partially resolve the optically thick core (60 AU at 150 pc).
3. Number of sources: 6
4. Coordinates:
4.1. 3 sources in Taurus (RA=04:30, DEC=+30)
3 sources in Oph (RA=16:30, DEC=-24)
4.2. Moving target: no
4.3. Time critical: no
5. Spatial scales:
5.1. Angular resolution: 0.4 arcsec
5.2. Range of spatial scales/FOV: up to 8 arcsec
5.3. Single dish: no
5.4. ACA: no
5.5. Subarrays: no
6. Frequencies:
6.1. Receiver band: Band 3, 6, 7, 9
6.2. Lines: see table below as (an incomplete) example
6.3. Spectral resolution (km/s): 0.2km/s
6.4. Spectral coverage (km/s or GHz): ~30-40 km/s disk
7. Continuum flux density: see also 3)
7.1. Typical value: 50-200 mJy
7.2. Continuum peak value:
7.3. Required continuum rms:
7.4. Dynamic range in image:
8. Line intensity:
8.1. Typical value: opacity limit of 0.05 at Tk=10--40 K, i.e.
0.5--2 K (deeper integration down to tau=0.02 for Band 6)
8.2. Required rms per channel: 0.5 K (deeper for Band 6)
8.3. Spectral dynamic range: low (in each channel...)
9. Polarization: not in this proposal
10. Integration time per setting:
Band 3: rms 1.7 K per hour, 12 hours per tuning, 2 tunings, 24 hours
Band 6: rms 0.4 K per hour, 3.3 hour per tuning, 3 tunings, 10 hours
Band 7: rms 0.5 K per hour, 1 hour per tuning, 3 tunings, 3 hours
Band 9: rms 0.3 K per hour, 0.4 hour per tuning, 3 tunings, 1.2 hours
Total: 38 hours per source, of which 14 at Band 6 and above.
11. Total integration time for program:
For 6 sources, 229 hours.
Column density with 1K km/s for each transition under LTE and
optically thin condition (Courtesy of Takakuwa at CfA) Line
transition Frequency 20 K 50 K HCO+ 1-0
89.188 1.39407967E+12 2.94454009E+12 CS 2-1 97.981
5.70174978E+12 1.11192032E+13 C18O 1-0 109.782
1.30730522E+15 2.70087115E+15 13CO 1-0 110.201
1.29839255E+15 2.68121637E+15 CO 1-0 115.271
1.1979902E+15 2.45996908E+15 C18O 2-1 219.560
5.3351956E+14 8.22277114E+14 13CO 2-1 220.399
5.30987708E+14 8.16971591E+14 CO 2-1 230.538
5.0249783E+14 7.57216339E+14 CS 5-4 244.935
3.56575535E+12 3.07323687E+12 HCO+ 3-2 267.558
4.27181797E+11 4.91656758E+11 C18O 3-2 329.331
5.16935379E+14 4.99454013E+14 13CO 3-2 330.588
5.1608577E+14 4.96851068E+14 CS 7-6 342.883
8.32157289E+12 2.88205239E+12 CO 3-2 345.796
5.07081138E+14 4.67465531E+14 HCO+ 4-3 356.734
5.62513526E+11 3.88788454E+11
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Review Phil Myers:transitions proposed for observation include only CO
and CS isotopomers, thus may not "completely" study "observable
chemistry" in disks--no N species are included.
Comment Ewine: Above table by Takakuwa is only illustrative for a few
dominant species. Many more molecules can be covered in one correlator
setting.
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Review v2.0:
Molecular surveys in 2-3 ``small'' samples from 0.5 to 3 msun
Authors: A.Dutrey, M.Momose, S.Guilloteau, E. van Dishoeck
Reviewer: John Bally
The Taurus fields are far north. Sources in Cha I or in one of the
other southern SFRs would be more appropriate targets.
It would be desirable to conduct full spectral scans of one or more
entire windows to determine the contents of large molecules. The
targets should be pre-selected for spectral richness using single-dish
observations. These multi-species searches could trace the
"snow-lines" for various species - at what radii do they disappear
from the gas phase? If gaps or other disk structures are seen, do
molecular abundances vary from the shadowed to the illuminated sides
of gaps?
Reply: You are too optimistic, the abundant molecules are already
known, from single-dish obsevrations. Unfortunately, even with the
ALMA sensitivity (eg see for example our PPV revieW), the chance to
detect the snow-line is very very low... Idem for the shadowed to
illuminated sides of gaps...
Disks around double stars such as L1551 IRS5 which has both
circumstellar and circumbinary disks should also be considered for
such studies.
Reply: YES, but this is not a proposal